The present invention is related to stock delivery systems for papermaking equipment, and in particular to a stock distributor and headbox arrangement to provide uniform consistency stock across a width of a papermaking machine.
Prior known headbox and stock delivery systems for papermaking machines all attempt to varying degrees to distribute the stock flow evenly and uniformly across the width of the papermaking machine. The amount of fiber per unit area (basis weight) is ideally constant across the width of the machine and along the machine direction.
The first step in transforming stock flow from a round pipe, which provides an initial delivery of the stock white water, to a thin rectangular shaped flow from the headbox (the stock jet) is to use a manifold device to distribute or feed the flow evenly into the headbox. Prior to the 1960's, a number of different types of flow spreaders were used, utilizing different piping arrangements. The primary problem with these prior art designs was that the flow was not uniform across the machine as the pipes closest to the incoming connection often received the most flow, starving the others. In the early 1960s, a tapered manifold system was developed for more uniform flow distribution. This system is still widely used today, but there often can be flow distribution issues.
A design where the tapered header is no longer used is also known, with the flow being supplied by a set of separate hoses to the headbox. Flow uniformity is achieved by using a cylindrical tank as the feed source with the hoses connected at a substantially similar height and in a symmetrical radial pattern to ensure uniform inflow conditions. These hoses are of equal length to ensure similar throughput. See U.S. Pat. No. 3,296,066.
To maintain a uniformity of paper in the machine direction, pressure pulsation dampening devices are often used in the stock delivery systems. Many of these incorporate a pressurized air chamber as the dampener and this chamber may be directly in contact with the stock flow (for example, as provided in U.S. Pat. No. 4,146,052) or may utilize a diaphragm interface (for example, as provided in U.S. Pat. No. 4,262,700).
So that a separate pulsation attenuator is not required, cylindrical stock feed tanks with radially distributed outlet hoses have also been combined with air chambers (such as disclosed in DE 431840 C2, EP 0631011 B1). With the advent of dilution profiling for basis weight control (for example, see U.S. Pat. Nos. 4,897,158; 4,909,904; and 5,196,091), this later design was also adapted by adding dilution water addition into the feed hoses (such as disclosed in DE 4005281 C1, U.S. Pat. No. 5,958,189).
The stock is then delivered from the headbox tube bank to the slice lip where it is directed onto the fabric of the papermaking machine, for example as provided in U.S. Pat. Nos. 4,137,124 or 4,783,241.
It would be desirable to provide an apparatus for the delivery of stock to the headbox of a papermaking machine, and from there onto a moving forming fabric, whereby non-uniformities in the resulting web are minimized and the physical properties of the web, especially with respect to basis weight and fiber orientation, are rendered as uniform as possible across the sheet.